Make Buttons as RadioButton

Make a group of buttons that can be selected and activate only one of them as RadioButton logic.

1.activity_button_group.xml

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:gravity="center_horizontal">

<Button
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:text="A"
    android:id="@+id/btn0"
    android:layout_gravity="center_vertical" />

<Button
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:text="B"
    android:id="@+id/btn1"
    android:layout_gravity="center_vertical" />

<Button
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:text="C"
    android:id="@+id/btn2"
    android:layout_gravity="center_vertical" />

<Button
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:text="D"
    android:id="@+id/btn3"
    android:layout_gravity="center_vertical" />
</LinearLayout>

2.MainActivity.java

public class ButtonGroupActivity extends Activity implements View.OnClickListener{

    private Button[] btn = new Button[4];
    private Button btn_unfocus;
    private int[] btn_id = {R.id.btn0, R.id.btn1, R.id.btn2, R.id.btn3};

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_button_group);

        for(int i = 0; i < btn.length; i++){
            btn[i] = (Button) findViewById(btn_id[i]);
            btn[i].setBackgroundColor(Color.rgb(207, 207, 207));
            btn[i].setOnClickListener(this);
        }

        btn_unfocus = btn[0];
    }

    @Override
    public void onClick(View v) {
        setForcus(btn_unfocus, (Button) findViewById(v.getId()));
        //Or use switch
        /*switch (v.getId()){
            case R.id.btn0 :
                setFocus(btn_unfocus, btn[0]);
                break;

            case R.id.btn1 :
                setFocus(btn_unfocus, btn[1]);
                break;

            case R.id.btn2 :
                setFocus(btn_unfocus, btn[2]);
                break;

            case R.id.btn3 :
                setFocus(btn_unfocus, btn[3]);
                break;
        }*/
    }

    private void setFocus(Button btn_unfocus, Button btn_focus){
        btn_unfocus.setTextColor(Color.rgb(49, 50, 51));
        btn_unfocus.setBackgroundColor(Color.rgb(207, 207, 207));
        btn_focus.setTextColor(Color.rgb(255, 255, 255));
        btn_focus.setBackgroundColor(Color.rgb(3, 106, 150));
        this.btn_unfocus = btn_focus;
    }
}